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Tannic acid (TA) is a bio-based high-molecular-weight organic molecule. Although biologically sourced, TA is a pollutant in industrial wastewater streams, and there is desire to find applications in which to downcycle this molecule. Many flame retardants (FRs) used in epoxy are synthesized from petroleum-based monomers. Various bio-based modifiers have been developed, but increasing the flame retardancy of the system without trade-offs with other properties has proved challenging. In this work, TA is incorporated into the thermoset. The molecular behavior of the system was dependent on the TA loading, with low concentrations causing the molecule to be surface-functionalized, while at higher concentrations the molecule was cross-linked into the network. The material was further characterized for its cross-link density, thermal stability, mechanical and thermomechanical properties and FR ability. In this work, TA was found to work well as an intumescent agent but did not reduce the heat release rate. The results of this study suggest that the external (hydrophilic surface-phenol groups) and internal (d-glucose and attached phenyl groups) structural regions of the TA molecule impact the FR ability of the molecule in epoxy separately. Maintaining the structural integrity of both regions is critical to the synergistic FR behavior of the molecule.

Natural fibers have been widely used for reinforcing polymers attributed to their sustainable nature, excellent stiffness to weight ratio, biodegradability, and low cost compared with synthetic fibers like carbon or glass fibers. Thermoplastic composites offer an advantage of recyclability after their service life, but challenges and opportunities remain in the recycling of natural fiber reinforced polymer composites (NFRPCs). This article summarized the effects of reprocessing/recycling on the material properties of NFRPCs. The material properties considered include mechanical performance, thermal properties, hygroscopic behavior, viscoelasticity, degradation, and durability. NFRPCs can generally be recycled approximately 4–6 times until their thermomechanical properties change. After recycling 7 times, the tensile strength of NFRPCs can decrease by 17%, and the tensile modulus can decrease by 28%. The mitigation approaches to overcome degradation of material properties of NFRPCs such as adding functional additives and virgin plastics are also discussed. The main challenges in these approaches such as degradation and incompatibility are discussed, and an effort is made to provide a rationale for reprocessing/recyclability assessment. Future applications of NFRPCs such as additive manufacturing and automotive part use are discussed.

Large amounts of plastics are discarded worldwide each year, leading to a significant mass of waste in landfills and pollution to soil, air, and waterways. Upcycling is an efficient way to transform plastic waste into high-value products and can significantly lessen the environmental impact of plastic production/consumption. In this article, current advances and future directions in plastic waste upcycling technologies are discussed. In particular, this review focuses on the production of high-value materials from plastic waste conversion methods, including pyrolysis, gasification, photoreforming, and mechanical reprocessing. Plastic waste compositions, conversion products, reaction mechanisms, catalyst selection, conversion efficiencies, polymer design, and polymer modification are also explored. The main challenges facing the adoption and scale-up of these technologies are highlighted. Suggestions are given for focusing future research and development to increase the efficiency of upcycling practices.

Sustainable, non-halogenated flame retardants are desired for a variety of industry applications. Lignin, an industrially processed wood derivative, has been examined as a potential sustainable flame retardant additive to polymer systems. Here, the lignin is phosphorylated using a pyridine-catalysed esterification reaction with diphenyl phosphoryl chloride to improve its char-forming abilities. The chemical modification of the lignin was characterised by nuclear magnetic resonance spectroscopy and showed the formation of phosphorylated structures on the lignin. The thermal decomposition profile and char-forming characteristics of the modified lignin and modified lignin–epoxy composites were investigated using thermogravimetry. The flammability performance of modified lignin–epoxy composites was tested using mass loss calorimetry. With the addition of 10% modified lignin, the peak heat release rate decreased by 40% and the total heat of combustion decreased by 20%. Scanning electron microscopy was used to investigate the char morphology of the post-flame test samples and showed closed cell foam structures.

In this paper the effect of two synthetic, pH-responsive co-polymers, U-PVPyPEGMA-H and Q-PVPyPEGMA-H, with pyridine and polyethylene glycol grafts, on silicic acid polymerization is presented. The scope of this work was to evaluate the impact of several experimental parameters, such as working pH, polymer MW, polymer concentration, state of the pyridine ring (non-protonated, protonated, quaternized) on the anticipated inhibitory and/or enhancement activity with regards to silicic acid autocondensation to produce amorphous silica. It was found that pH substantially influences the silicification reaction, either in the absence or presence of the polymers. pH also affects the protonation state of the pyridine N atom. For example, pH switching from 5.0 to 7.0 transforms U-PVPyPEGMA-H from a silica formation catalyst (pH = 5.0) to a silicic acid stabilizer (pH = 7.0). Concentration enhances the role of the polymers, either as silicic acid stabilizers or catalysts. Polymer MW appears to have no effect on their activity either as stabilizers or catalysts. Polymer entrapment in the precipitated amorphous silica matrix occurs under these experimental conditions, affecting particle size, morphology and tendency for aggregation. The state of the N atom on the pyridine ring (non-protonated, protonated, quaternized) exhibits a profound effect on silicic acid autocondensation to produce amorphous silica. Based on our results, a “free” (non-protonated) pyridine ring induces silica inhibition, whereas protonation or quaternization enhances silica formation.

Tannic acid (TA) is a bio-based high molecular weight organic (HMWO), aromatic molecule. Although biologically sourced, TA currently pollutes industrial wastewater streams, and there is an industrial desire to find applications to downcycle this molecule. Epoxy thermosets have revolutionized many industries, but are too flammable to be used in many applications without additives which augment its flame retardancy (FR). Many flame retardants used in epoxy thermosets are synthesized from petroleum-based monomers leading to significant environmental impacts at the industrial scale. Various bio-based modifiers have been developed to improve the FR of the epoxy resin; however, increasing FR of the system without trade-offs with other properties has proven to be challenging. In this work, TA was incorporated into the thermoset. The molecule was found to increase the intumescence of the system without significant changes to the Tg and strength paving the way for biological intumescent agents to be used industrially.